sink-input/source-output: Prevent filter sink/source cycles

Misbehaving clients can try to set a filter sink to output to
itself, leading to crashes later on. This patch protects us from that.

Thanks to Roman Beslik for testing and finding an error in the first
version of this patch.

Tested-by: Roman Beslik <rabeslik@gmail.com>
BugLink: https://bugs.freedesktop.org/show_bug.cgi?id=44397
Signed-off-by: David Henningsson <david.henningsson@canonical.com>

2 files changed, 34 insertions, 0 deletions

diff --git a/src/pulsecore/sink-input.c b/src/pulsecore/sink-input.c
index b8412bd0..f6f7324c 100644
--- a/src/pulsecore/sink-input.c
+++ b/src/pulsecore/sink-input.c
@@ -1383,6 +1383,17 @@ pa_bool_t pa_sink_input_may_move(pa_sink_input *i) {
     return TRUE;
 }
 
+static pa_bool_t find_filter_sink_input(pa_sink_input *target, pa_sink *s) {
+    int i = 0;
+    while (s && s->input_to_master) {
+        if (s->input_to_master == target)
+            return TRUE;
+        s = s->input_to_master->sink;
+        pa_assert(i++ < 100);
+    }
+    return FALSE;
+}
+
 /* Called from main context */
 pa_bool_t pa_sink_input_may_move_to(pa_sink_input *i, pa_sink *dest) {
     pa_sink_input_assert_ref(i);
@@ -1396,6 +1407,12 @@ pa_bool_t pa_sink_input_may_move_to(pa_sink_input *i, pa_sink *dest) {
     if (!pa_sink_input_may_move(i))
         return FALSE;
 
+    /* Make sure we're not creating a filter sink cycle */
+    if (find_filter_sink_input(i, dest)) {
+        pa_log_debug("Can't connect input to %s, as that would create a cycle.", dest->name);
+        return FALSE;
+    }
+
     if (pa_idxset_size(dest->inputs) >= PA_MAX_INPUTS_PER_SINK) {
         pa_log_warn("Failed to move sink input: too many inputs per sink.");
         return FALSE;
diff --git a/src/pulsecore/source-output.c b/src/pulsecore/source-output.c
index fbfea9c1..cd7981c9 100644
--- a/src/pulsecore/source-output.c
+++ b/src/pulsecore/source-output.c
@@ -1160,6 +1160,17 @@ pa_bool_t pa_source_output_may_move(pa_source_output *o) {
     return TRUE;
 }
 
+static pa_bool_t find_filter_source_output(pa_source_output *target, pa_source *s) {
+    int i = 0;
+    while (s && s->output_from_master) {
+        if (s->output_from_master == target)
+            return TRUE;
+        s = s->output_from_master->source;
+        pa_assert(i++ < 100);
+    }
+    return FALSE;
+}
+
 /* Called from main context */
 pa_bool_t pa_source_output_may_move_to(pa_source_output *o, pa_source *dest) {
     pa_source_output_assert_ref(o);
@@ -1172,6 +1183,12 @@ pa_bool_t pa_source_output_may_move_to(pa_source_output *o, pa_source *dest) {
     if (!pa_source_output_may_move(o))
         return FALSE;
 
+    /* Make sure we're not creating a filter source cycle */
+    if (find_filter_source_output(o, dest)) {
+        pa_log_debug("Can't connect output to %s, as that would create a cycle.", dest->name);
+        return FALSE;
+    }
+
     if (pa_idxset_size(dest->outputs) >= PA_MAX_OUTPUTS_PER_SOURCE) {
         pa_log_warn("Failed to move source output: too many outputs per source.");
         return FALSE;